I think Kanai's Cube is only found in Adventure Mode, in Act 3. You can start combining and de-socketing gems in the latter half of Act 2 once you rescue the jeweler from the sewers.

During the story mode, I've noticed that I keep getting better and better equipment all the time, so there's little need to tweak the items you do find. I haven't used her yet, I think this option is more useful later in the game. You can also use Myriam (NPC in the town) to re-enchant your items, essentially re-rolling some of their stats. (I'm not 100% sure if they are better than the ones you can buy, but selling equipment pays back so little gold it's really not worth it.) At some point you should start salvaging crafting materials (at the Blacksmith) from the equipment you find, as you can get good equipment by crafting them (at the Blacksmith). I found this to be very helpful - I can have passives and rarely used skills on the less convenient buttons. This allows you to bind any skill you have unlocked to any button on our controller. Make sure to go into your game settings and turn on the Elective Mode. However, if you have equipment that has a % chance to do something (like slow down the enemy), that will work more often if you have a higher rate of attack, so sometimes it's better to have a lower dps but a higher rate of attack. Note that having a higher rate of attack is already calculated into your damage per second (dps). Since you don't easily see all the info for items on consoles (I play on Xbox), use the sword-icon, shield-icon and plus-icon under your character portrait to compare weapons, armor and other equipment to see if switching them improves your damage output per second (sword-icon), toughness (shield-icon) and/or healing (plus-icon).

(You should play at the hardest difficulty level you can, as it provides more/better loot and more XP.) I found that life per hit and life per second items are invaluable at early levels, especially for ranged character, especially at the hardest difficulty level. For the most part, you want to maximize your main stat (Str for Barbarian and Crusader, Dex for Monk and Demon Hunter, Int for Witch Doctor and Wizard) since this affects the damage for all your skills. I guess these are the main things to consider: I've been playing D3 for a week now and I'm also in the story mode. It's a bit difficult to find advice for the story mode and for levels 1-70.

Diablo 3 reaper of souls ps3 secrets